In a surface treatment, such as plating, chemical conversion treatment and soon, a cleaning process is conventionally carried out. For example, a rinsing process is carried out for removing drug solution from a surface-treated product by multi-stage water washing of maceration and/or shower of water. In the water washing process for the surface treatment, the drug solution adhered to the product is diluted and removed. Therefore, not only a large volume of water is necessary but also wastewater treatment is required.
It is, therefore, proposed in a conventional cleaning method to increase a number of water washing tanks so as to suppress the volume of the washing water. Alternatively, as disclosed in Japanese Examined publication No. S62-48756, it is proposed to provide a reduced-pressure distillation device in order to achieve no wastewater.
The inventor of the present invention has proposed ideas (not published before the present invention) in a prior Japanese Patent Application No. 2009-162797 (published under Publication No. 2011-016079) and in another prior Japanese Patent Application No. 2010-094897 (not yet published). In the above prior Patent Applications, the inventor proposed a cleaning and drying method and apparatus, according to which cleaning fluid (in a pressurized and superheated condition) is injected to a product to be cleaned so that a cleaning and drying process can be carried out in a shorter time period.
According to the above prior art (JP S62-48756), since the reduced-pressure distillation device is provided to achieve no wastewater, it is a problem that a cost for the apparatus is increased or the apparatus may become larger.
According to the prior Patent Applications by the same inventor (not belonging to the prior arts), it is possible to clean and dry the product in a shorter time period by injecting the cleaning fluid of the pressurized and superheated condition. This is effective for a physical cleaning method to remove fats and oils or extraneous material adhered to the product (such as, electronic parts and components, mechanical parts and components). However, it is not possible to achieve cleaning quality, which is required for water washing for a surface-treated product.
The inventor of the present invention proposed a small-sized cleaning apparatus in the above prior application (application No. 2010-094897), which is not published at the date of application of the present invention.
According to the cleaning apparatus of the above prior application, cleaning liquid is pressurized and injected into a cleaning and drying chamber covering a product to be cleaned. A boiling point of the cleaning liquid in the atmospheric pressure is remarkably changed in a pressurized condition. And the cleaning liquid is lyophobic to oils (insoluble in fats and oils) and selected from such liquids, as water, hydrated alcohol, fluorine compound (for example, hydrofluoric carbon (HFC), hydrofluoric ether (HFE)) and so on, wherein the boiling point thereof (saturation temperature) is higher than 40° C. in the atmospheric pressure.
The injected cleaning liquid (which is pressurized and superheated) is instantaneously vaporized and expanded on a surface of the product to be cleaned, in order to remove contamination and/or fats and oils from the surface of the product by actions of flow speed and heat energy of the cleaning liquid by expansion. Since molecules of the injected cleaning liquid are lyophobic to fats and oils, collision force generated by the vaporization and expansion acts as repulsive force to thereby work on removing the fats and oils.
In addition, volume of the vapor of the cleaning liquid injected into the cleaning and drying chamber (in the atmospheric pressure) is larger than a space volume of the cleaning and drying chamber, so that the effect for wiping out and removing the Fats and oils can be increased.
FIG. 15 is a schematic view showing a cleaning and drying apparatus of the prior application. The cleaning and drying apparatus will be explained as a related art. In FIG. 15, a product 1 to be cleaned, to which fats and oils are adhered, is transferred by a conveyer 2 to a cleaning and drying position. A tank 5 for pooling cleaning liquid 4 is provided in the cleaning and drying apparatus.
In the tank 5, the cleaning liquid 4 is pooled, a boiling point of which is remarkably changed in the atmospheric pressure and in a pressurized condition. The cleaning liquid is lyophobic to oils (insoluble in fats and oils) and selected from such liquids, as water, hydrated alcohol, fluorine compound (for example, hydrofluoric carbon (HFC), hydrofluoric ether (HFE)) and so on, wherein the boiling point thereof (saturation temperature) is higher than 40° C. in the atmospheric pressure.
The cleaning liquid 4 from the tank 5 is pressurized by a liquid pump 6 and supplied to an injection nozzle 3 via a fluid supply pipe 7. A heat exchanger 8 is provided at an intermediate point of the fluid supply pipe 7, so that the cleaning liquid is heated to a condition of superheated cleaning liquid, the temperature of which is higher than the boiling point (the saturation temperature) in the atmospheric pressure, more preferably, the temperature of which is close to a boiling point of such a pressurized condition.
The cleaning and drying process is carried out at the same time, by injecting the pressurized and superheated cleaning liquid 4 from the injection nozzle 3 to the product 1 to be cleaned, which is located in the atmospheric pressure. A cleaning and drying chamber 10 is provided for covering the product 1. A vapor collecting opening 13 is provided at a downward side of the chamber 10, so that the vapor of the cleaning liquid 4 injected from the injection nozzle 3 can be collected. A volume of the cleaning liquid injected from the injection nozzle into the cleaning and drying chamber 10 in the atmospheric pressure is made larger than a space volume of the cleaning and drying chamber 10.
The cleaning liquid 4 injected from the injection nozzle 3 and the contamination removed from the product 1 are collected in the tank 5. When continuously repeating the cleaning and drying process, the contamination from the products 1 will be accumulated in the tank 5.
The contamination (fats and oils) accumulated in the tank 5 are not dissolved in the cleaning liquid, those fats and oils come to the surface in the tank 5, when specific gravity of those fats and oils is smaller than that of the cleaning liquid. As a result, the fats and oils form a layer at the surface, while the cleaning liquid 4 remains in the lower portion in the tank 5. Therefore, the tank 5 has a function for separating the fats and oils from the cleaning liquid. The fats and oils at the surface layer are discharged through a drain pipe 24, so that the contamination accumulated in the tank 5 is finally discharged from the tank 5.
According to the cleaning and drying method and apparatus of the above prior application, the cleaning liquid 4, such as the water, the hydrated alcohol and so on, the boiling point of the atmospheric pressure (the saturation temperature) of which is higher than that of the fluorine compound, the vapor of the cleaning liquid hardly condenses on the surface of the product to be cleaned. At a portion of the surface, at which a layer of the condensate is formed, effect for removing the fats and oils may be decreased and the cleaning liquid 4 may remain on the surface (that is, it may cause an insufficient drying process).
On the other hand, when the fluorine compound, the boiling point of the atmospheric pressure (the saturation temperature) is lower than that of the water, is used, the vapor pressure is high and the layer of the condensate is hardly formed compared with the water. Therefore, even when the layer of the condensate is formed, the condensate is easily vaporized under the atmospheric pressure. Although not causing the insufficient drying, global warming material may be discharged into the air. It is, therefore, necessary to surely collect the vapor of the cleaning liquid 4.
According to the cleaning and drying apparatus of the prior application (the related art), it is difficult for the vapor collecting opening 13 to completely collect the vapor of the cleaning liquid 4 injected from the injection nozzle. In addition, the vapor of the cleaning liquid 4 easily condenses. Therefore, the effect for removing the fats and oils is decreased at the portion, at which the condensate is formed. Furthermore, the insufficient drying may be caused when the cleaning liquid 4 remains on the surface of the product to be cleaned. Furthermore, it may have a problem that the global warming material (the fluorine compound) may be discharged into the air.